Listeriolysin O-dependent bacterial entry into the cytoplasm is required for calpain activation and interleukin-1 alpha secretion in macrophages infected with Listeria monocytogenes.

Abstract

Listeriolysin O (LLO), an hly-encoded cytolysin of Listeria monocytogenes, plays an essential role in the entry of L. monocytogenes into the host cell cytoplasm. L. monocytogenes-infected macrophages produce various proinflammatory cytokines, including interleukin-1 alpha (IL-1 alpha), that contribute to the host immune response. In this study, we have examined IL-1 alpha production in macrophages infected with wild-type L. monocytogenes or a nonescaping mutant strain deficient for LLO (Delta hly). Expression of IL-1 alpha mRNA and accumulation of pro-IL-1 alpha in the cytoplasm were induced by both strains. In contrast, the secretion of the mature form of IL-1 alpha from infected macrophages was observed in infection with wild-type L. monocytogenes but not with the Delta hly mutant. A recovery of the ability to induce IL-1 alpha secretion was shown in a mutant strain complemented with the hly gene. The Toll-like receptor (TLR)/MyD88 signaling pathway was exclusively required for the expression of pro-IL-1 alpha, independently of LLO-mediated cytoplasmic entry of L. monocytogenes. The LLO-dependent secretion of mature IL-1 alpha was abolished by addition of calcium chelators, and only LLO-producing L. monocytogenes strains were able to induce elevation of the intracellular calcium level in infected macrophages. A calcium-dependent protease, calpain, was implicated in the maturation and secretion of IL-1 alpha induced by LLO-producing L. monocytogenes strains based on the effect of calpain inhibitor. Functional activation of calpain was detected in macrophages infected with LLO-producing L. monocytogenes strains but not with a mutant strain lacking LLO. These results clearly indicated that LLO-mediated cytoplasmic entry of bacteria could induce the activation of intracellular calcium signaling, which is essential for maturation and secretion of IL-1 alpha in macrophages during L. monocytogenes infection through activation of a calcium-dependent calpain protease. In addition, recombinant LLO, when added to macrophages infected with the Delta hly strain, could induce calcium influx and IL-1 alpha secretion at doses exhibiting cytolytic activity, suggesting that LLO produced by intracellular L. monocytogenes may be implicated in induction of calcium influx through pore formation.

• Authors: Sita R Dewamitta, Takamasa Nomura, Ikuo Kawamura, Hideki Hara, Kohsuke Tsuchiya, Takeshi Kurenuma, Yanna Shen, Sylvia Daim, Takeshi Yamamoto, Huixin Qu, Shunsuke Sakai, Yanting Xu, Masao Mitsuyama
• Journal: Infection and immunity (Infect Immun) Vol. 78 Issue 5 Pg. 1884-94 (May 2010) ISSN: 1098-5522 [Electronic] United States
• PMID: 20194588 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Bacterial Toxins
• Heat-Shock Proteins
• Hemolysin Proteins
• Interleukin-1alpha
• Virulence Factors
• Calpain
• hlyA protein, Listeria monocytogenes

Topics

• Animals
• Bacterial Toxins (metabolism)
• Calpain (biosynthesis)
• Cytoplasm (microbiology)
• Female
• Gene Knockout Techniques
• Genetic Complementation Test
• Heat-Shock Proteins (deficiency, metabolism)
• Hemolysin Proteins (deficiency, metabolism)
• Interleukin-1alpha (metabolism)
• Listeria monocytogenes (pathogenicity)
• Macrophages (microbiology)
• Mice
• Mice, Inbred C57BL
• Virulence Factors (metabolism)